Why is Wirtanen's 2018 Apparition Historic?

Wirtanen makes a very close approach to the Earth

  • Occurs Dec 16, 2018
    • Only 4 days after perihelion
    • The comet is near its brightest
  • Geocentric Distance
    • 0.0777 AU
    • 30 Lunar distances
    • 11.5 million km
    • 7.1 million miles
  • 10th closest comet in modern times
    • Few of the others reached naked eye brightness

Wirtanen is inherently relatively bright

  • Hyperactive comet
    • Has higher production rates than typical comets of the same size
  • Predicted to reach naked-eye brightness around close approach
    • In the most optimistic scenario, it could remain there for several weeks

Observing conditions are excellent

  • Near opposition at close approach
    • Visible most of the night around close approach (North and South hemispheres)
    • Visible for many hours for months before and after close approach

Great apparition for studying the comet

  • Small geocentric distance offers close-up views
    • High spatial resolution (1 arcsec spans 57 km at close approach)
    • Unique opportunity to image and measure the inner coma
    • Use radar characterize the nucleus itself
  • Brightness allows many techniques to be used
    • High spectral resolution spectroscopy
    • Detailed composition measurements
  • Observability allows extensive temporal studies
    • Long-term secular behavior
    • Rotational variability
    • Outburst monitoring
    • Solar phase dependencies
Excellent opportunity to characterize this potential spacecraft target!


Great comet for education and public outreach

  • Amateur observers can contribute to scientific studies
  • Comet's high profile provides a means for educating the public about comets
  • Wirtanen can be the centerpiece for star parties